Complete Misfire on Three Cylinders

[Patcon]

Also the valves could be rotating between adjustments.  If the seats are inconsistent then your lash would change based on orientation

[Captain Obvious]

Well with the valves lapped into place, I know both the valve faces and the seats are consistent now. So even if the valves rotate, they should be fine. In fact, some cars, they try to rotate the valves on purpose. Is that not the case on the Z?

[Captain Obvious]

So I've started addressing the block. Cleaning things up in preparation for the head reinstall.

I've got a hodge-podge of pistons in there. I've got four of these:

One of these:

And at cylinder #1, I've got one of these:

No real surprises there, I guess. I know my PO had been in there, so I was kinda expecting some stuff like that.

I did notice that the cylinder 1 marked "STD" does stick up out of the block by about fifteen thousandths at TDC, but the one marked 34 at position 6 sits flush. So I've got some mismatching on compressed volume there, but not enough that I'm going to do anything about it right now. I can't rotate the engine right now because I've got the timing chain wedged, but I suspect all of the pistons except the "STD" one do not protrude above the block deck at TDC.

So anyone see anything "project stopping horribly wrong" with that combination of pistons? Is there any rhyme or reason to the "34" or "45" markings?

[240260280]

I've seen numbers on the block and on pistons. I think it was how they selected best fits in plant. The std was probably a repair piston.

[Captain Obvious]

I also took some quick and dirty measurements on the distances between pistons and valves...

The valves, when closed, are about .185 below the head bottom surface:

And the dish depth on the pistons are about .115. Don't have a pic of that measurement, but it was like this with the caliper in the center of the piston:

So... The bottom line is there is about .300 clearance plus the head gasket thickness between a closed valve and piston when the piston is at TDC. That distance may have saved me a whole lot of crunching.

Also, assuming that valve opening distance is greater than .380-ish, I believe this confirms that the stock motor IS an interference design?

[Zed Head]

You'd have to consider the angle of the valve to get its extension toward the piston but it seems close.

[Zed Head]

You could measure a valve's projection on that head you have assembled.  Then you'll have all of the numbers.

[Captain Obvious]

Yeah, I was planning to measure the projection once I got further along with the head reassembly. Based on the valve lift number you posted from the FSM, it's close either way.

But with a closed clearance of approx. .380, I guess it's easier to believe that all my valves stopped in a position where there was no collision. Still thinking about that five mile drive home with only half the cam spinning!!  

[Captain Obvious]

So here's a question for today. If you look closely at this water jacket hole... Up by the timing chain and cylinder one, on the left side of the engine. It's threaded.

The paper towel wad is stuffed into the head bolt hole, and the other hole just goes down into the water jacket. There's a corresponding hole in the gasket and the head. but question is... Why is it threaded?  :

I tried to measure the thread size and didn't come up with anything standard. It's a very loose fit on M10-1.5, but it's not big enough to be M12. So it's either a badly corroded out M10, or it's something unusual.

Any ideas?

[Dave WM]

rebuilder thought is was a head bolt hole, and chased it.

[Patcon]

Sometimes people will block holes like that to change or restrict water flow. Could have been flush plugged or sometimes they will flush plug them and then drill a hole for lower flow.

Just a guess...

[Av8ferg]

rebuilder thought is was a head bolt hole, and chased it.

I agree, we’ve already established the PO wasn’t all that good this would be the most plausible reason.


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